Method of recovering quinoline bases



United States Patent Ofiice 3,390,151 Patented June 25, 1968 3,390,151 METHOD OF RECOVERING QUINOLINE BASES Philip X. Masciantonio, Penn Township, Westmoreland County, and William E. Peoples, North Huntingdon Township, Westrnoreland County, Pa., assignors to United States Steel Corporation, a corporation of Delaware Filed Sept. 16, 1965, Ser. No. 487,793 1 Claim. (Cl. 260-283) ABSTRACT OF THE DISCLOSURE A cyclic method of recovering quinoline bases from a crude coal tar fraction. The tar is treated with monopyridinium sulfate to obtain an extract of quinoline bases. The extract is treated with pyridine to spring the quinoline bases and produce dipyridinium sulfate. The latter is fractionated to recover pyridine and monopyridinium sulfate for re-use in the process.

This invention relates to an improved method of recovering quinoline bases from coal-tar distillate.

Quinoline bases are a valuable group of heterocyclic nitrogen compounds used commercially in pharmaceuticals, dyes, insecticides, and other chemical products. They occur in the 230 to 270 C. fraction of coal tar, and they include such compounds as quinoline, isoquinoline, and the various methylquinolines. Conventionally quinoline bases are recovered from coal tar by extraction from the particular fraction with an aqueous mineral acid solution. The acid extract then is neutralized with a base, such as caustic soda, and the crude quinoline bases thereby sprung and decanted as a separate phase. The crude quinoline bases may be sold as a mixture, or the individual compounds may be isolated by fractional distillation.

Recovery of quinoline bases by the foregoing technique has disadvantages. Mineral acid and base are consumed in the extraction and neutralization steps of the process, and there is problem in disposing of the resulting waste neutralized phase. The acid is not selective as to the types of tar bases extracted from the fraction, and it is difficult to obtain quinoline bases of high purity. Sulfuric acid is the cheapest and most widely used acid for the extraction step, but its use necessitates careful control to avoid sulfonation of the extract. A dilute acid must be used, adding to the volume of waste for disposal.

An object of the present invention is to provide an improved method of recovering quinoline bases, which method is completely cyclic in operation, thereby avoiding acid consumption and the resulting waste disposal problem.

A further object is to provide a method of the foregoing type which produces quinoline bases of improved quality.

A further object is to provide a method of recovering quinoline bases in which concentrated acid is used, yet the sulfonation problem is avoided.

In the drawing:

The single figure is a schematic flow sheet of our quinoline base recovery method.

We introduce the crude coal tar fraction which contains the quinoline bases (the 230-270" C. fraction) to an extraction vessel 10, along with an aqueous monopyridinium sulfate solution. Quinoline bases are present in the tar fraction at a concentration of about lO percent by weight. We can use a solution of monopyridinium sulfate which has a concentration in a range as broad as 1 to percent by weight, but we prefer a concentration between 20 and 70 percent, and we consider about 45 percent optimum. The mole ratio of quinoline bases to monopyridinium sulfate in the extraction vessel can be in a range of 0.1/1 to 1/1, but we prefer about 0.3/1 to 0.7/1 and we consider about 0.7/1 optimum. The temperature must be below C., but we prefer a temperature of 20 to 80 C. and we consider about 30 to 50 C. optimum. We mix the materials in the vessel for at least about 5 minutes or preferably about 15 minutes, and we allow the materials to stand at least about 5 minutes after mixing or preferably about 15 minutes. The materials separate into two phases: (1) a washed tar fraction, and (2) an aqueous extract which contains the quinoline bases.

We decant the aqueous extract from vessel 10 and introduce it to a springing vessel 12, along with pyri dine in a quantity sufficient to convert the monopyridinium sulfate to dipyridinium sulfate. The pyridine can be either anhydrous or an aqueous solution in the broadest sense, but we prefer the aqueous solution produced in our regeneration step, hereinafter described. The temperature should be below 100 C., but we prefer a temperature of 20 to 80 C. and we consider 30 to 50 C. optimum. We stir the extract slowly while adding pyridine, and the crude quinoline bases form a separate oil phase. From a consideration of the relative basicity of pyridine and quinoline, we would expect an equilib rium mixture of pyridine and quinoline to form in both the aqueous and oil phases in the ratio of about 1.5 quinoline to l pyridine. Unexpectedly we obtain an oil phase which consists predominantly of quinoline bases, that is, a mole ratio of quinoline bases to pyridine of about 2.4/1. The high ratio enables us later to sepa rate the quinoline and pyridine economically without having to handle excessive quantities of pyridine. We believe the high ratio is explained by the relative solubility of quinoline and pyridine in water. Pyridine is completely miscible with water, while quinoline is only slightly soluble. Therefore quinoline is continuously removed from the system as a separate phase, and the equilibrium ratio of quinoline and pyridine is not attained. The two phases are easily separated because of the relatively high density of the aqueous phase.

We decant the oil phase from the aqueous phase in the springing vessel 12 and introduce the latter to a fractionating device 13, which can be either a simple one-tray still or a multi-tray fractionating column. In this device we decompose the aqueous dipyridinium sulfate into monopyridinium sulfate and pyridine and we separate these substances into an aqueous monopyridinium fraction and an aqueous pyridine fraction. We recycle the first fraction to the extraction vessel 10 and the second fraction to the springing vessel 12. We introduce the oil phase from the springing vessel 12 to a fractionating device 14 where We separate the quinoline bases from the pyridine. We recycle the latter to the springing vessel 12. The quinoline bases can either be a finished product or the individual compounds can be isolated.

As a specific example to demonstrate our invention, we prepared an extracting reagent by adding 102 grams of pyridine to 398 grams of 30 percent sulfuric acid. We introduced to the extraction vessel 1000 grams of crude coal tar fraction (BO-270 C.) along with 446 grams of monopyridinium sulfate prepared as we described. The temperature was about 35" C. We mixed the materials for 15 minutes and let them stand another 15 minutes after mixing, after which we decanted the aqueous extract from the tar fraction. In this manner we obtained 905.5 grams of washed tar fraction and 540.5 grams of aqueous extract. Chemical analysis of the tar before and after the extraction step showed the composition to be as follows:

Composition, mole percent 1 Next we introduced the aqueous extract to tne springing vessel, along with 191 grams of aqueous pyridine (containing 104 grams of water and 87 grams pyridine), and stirred them slowly. We obtained 126.8 grams of an oil phase (quinoline bases plus pyridine) and 604.7 grams of an aqueous phase (aqueous dipyridinium sulfate). We fractionated the oil phase and obtained 32.3 grams of aqueous pyridine (containing 9 grams of water and 23.9 grams pyridine) and the remainder quinoline bases. We also fractionated the aqueous phase and obtained 158.7 grams of aqueous pyridine and 446 grams of aqueous monopyridinium sulfate. The pyridine and ionopyridinium sulfate were available for recycling, as shown in the flow diagram.

It is apparent our method could also be used to recover nitrogen bases from streams other than coal tar fractions. For example we could treat petroleum fractions or materials which result from chemical processing. We can recover nitrogen bases other than quinoline, as

long as these bases are no stronger than pyridine. Sul- 3 furie acid used in making up the extracting solution might be replaced by other acids, such as sulfurous, oxalic, tartaric, chloroacetic, sodium bisulfite, or phosphoric. The extracting medium might be regenerated other than by distillation, for example by hot countercurrent extraction with a solvent such as xylene. Therefore we do not wish to be limited by the disclosure set forth, but only by the scope of the appended claim.

We claim: 1. A method of recovering quinoline bases from a crude 230-270 C. coal tar fraction comprising:

mixing aqueous monopyridinium sulfate with said tar fraction in a mole ratio of said bases to said sulfate in the range of 0.1/1 to 1/1, thereby obtaining an aqueous extract of said bases; treating said extract with pyridine to spring said bases as an oil phase of said bases with pyridine and produce an aqueous phase of dipyridinium sulfate; fractionating said oil phase to separate pyridine therefrom and recover the quinoline bases; fractionating said aquous phase to obtain monopyridinum sulfate and pyridine; recycling pyridine obtained in the fractionating steps to treat said extract; and recycling monopyridinium sulfate obtained in the second-named fractionating step to mix with said tar fraction.

References Cited UNITED STATES PATENTS 2,206,198 7/1940 Molinari 260-290 X 2,518,353 8/1950 McKinnis 260'290 X 2,720,526 10/1955 Sweeney 260-283 X 2,799,678 7/1957 Sweeney 260283 X 2,999,794 9/1961 Foster 260283 X 5 NICHOLAS S. RIZZO, Primary Examiner.

D. G. DAUS, Assistant Examiner. 

